Method and apparatus for viscous processing

ABSTRACT

Method and apparatus for processing an exposed photographic film in which the film has a thin coating of a processing composition applied thereto after which it is maintained in a processing zone having a controlled atmosphere for a predetermined period of time and then has the composition removed therefrom. The atmosphere of the processing zone is maintained at a substantially constant wet bulb temperature and at a relative humidity which is not greater than the relative humidity at which the coating of processing composition is in equilibrium therewith.

7 a mi v ijit ates Patent [111 3,599,554

[7 2] Inventors Marcel Frans Aelterrnan; [56] References Cited Louis Achilles Meeussen, both oi Mortsel, UNITED STATES PATENTS 21 A l N gj g'g 3,087,405 4/1963 Sachs et al. 95/94 Whig 1968 3,157,103 11/1964 Lowry etal... 95/89 Patented g 17,1971 3,177,790 4/1965 Turner et al. 95/89 [73] Assignee Gevaert-AGFA NQV. Primary ExaminerSamuel S. Matthews Mortsel, Belgium Arsistant Examiner-- Fred L. Braun [32] Priority July 3, i967 Att0rneyWilliam J. Daniel [33] Great Britain [31] 30,626/67 W V W W W T 7 ABSTRACT: Method and apparatus for processing an ex- 54 METHOD AND APPARATUS F011 VHS COUS i fil-n? m 2 1 has 2 2 1 9f PRQQCESSMNG a processing composmon app 1e t ereto a ter w 1c it is 16 maims 5D in m maintained 1n a processmg zone havmg a controlled atw E mosphere for a predetermined period of time and then has the [52] USJCH 95/8951, composition removed therefrom. The atmosphere of the 34/50, 118/65 processing zone is maintained at a substantially constant wet [51] lint. (1i 603d 5/00 bulb temperature and at a relative humidity which is not [50] Field of Search 95/89, 94; greater than the relative humidity at which the coating of processing composition is in equilibrium therewith.

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PATENTED nus: 11971 3 599554 sum 2 [1F 3 PATENIEU ms: 1 an sum 3 or 3 FIG. 5

ME'llllliUll) AND APPARATUS FOR VISCOUS PROCESSHNG The present invention relates to a method and an apparatus for the viscous processing of an exposed photographic web.

Apparatus for the viscous processing of photographic Webs are known. They generally comprise an extrusion hopper mounted adjacent the web path in a processing zone for the extrusion of a thin layer of processing composition onto the exposed surface of the web, and a spray jet in said zone for the removal of the processing coating from the web after it has remained a determined time thereon.

In processing apparatus of this type, fresh processing solutions are always used so that the usual problems of seasoning, solution control, and replenishment are eliminated. The processing compositions are viscous developing or fixing solu tions which are the normal type of concentrated solutions to which a thickening agent has been added in an amount required to impart the desired viscosity to the solutions for good results without impairing the chemical properties of the solutions.

In order to insure control over the processing cycle and to achieve reproducible results, it is necessary to closely control the temperature and the humidity in the processing zone, since it is essential to maintain the wet bulb temperature and the relative humidity in said zone at a substantial constant value.

Since the maintaining of the processing atmosphere at substantial constant wet bulb temperature is found in literature relative to viscous photographic processing and also for the sake of conciseness, reference will be made thereto hereinafter. it is clear that actually two of the three parameters which determine an atmosphere, viz the wet bulb temperature, the dry bulb temperature and the relative humidity, must be controlled in order to guarantee a determined condition of the processing atmosphere. The relation between said three parameters may be read on a psychometric chart.

it is known to accomplish the control over the processing cycle by maintaining the processing zone in a saturated condition by means of hot water which is discharged through wash nozzles and which, in addition to the step of thoroughly washing the film, serves the function of maintaining the atmosphere in the developing zone saturated with water vapor, see eg the control of the apparatus described in US. Pat. specifications Nos. 3,117,508 of E. H. Deann and R. J. Wilson issued Jan. 14, 1964 and 3,177,790 of J. R. Turner and R. J. Wilson, issued Apr. 13, 1965. The application of said method seems quite attractive, since an atmosphere saturated with water vapor can be easily maintained and controlled.

The described method, however, shows several disad' vantages.

A saturated atmosphere requires an excellent thermic insulation of the processing zone to avoid excessive condensation. it is especially important to prevent droplets of condensate from contacting the web surface or the viscous coating thereon, and practice proves that it is almost impossible to completely avoid this phenomenon. The maintenance of the saturated atmosphere in the mentioned apparatus is also impeded by the slow circulation of the saturated air. In fact, the air is circulated only by virtue of the downwardly projected water particles from the wash nozzles, which carry along the surrounding air.

The processing in an atmosphere saturated with water vapor requires the use of processing compositions having a relative high viscosity, say 2,000 to 4,000 centipoise at 30 C., since at lower viscosity the processing composition becomes excessively diluted by the absorption of water from the saturated atmosphere, whereby it will move on the surface producing drag" and other undesired effects.

The preparation of liquid compositions of the mentioned viscosity cannot occur with conventional stirring apparatus, and the removal of air bubbles from the composition causes difficulties. The heating of the composition before it is fed to the hopper for extrusion requires special heat exchangers in order to obtain a sufficient heat transfer. The switching over to another processing composition and the cleaning of the processing apparatus require relatively much time since the composition is difiiculty removable.

The circulation velocity of the saturated air is low, since the movement thereof is only caused by spray jets drawing the air downwardly through the channel wherein they are mounted.

Finally, as a consequence of the constant temperature at which the humidifying water is sprayed into the atmosphere, the apparatus is very sensitive to change in the ambient temperature and relative humidity, and moreover a relative long period is required after the apparatus has been started to operate, before constant processing conditions have established.

The object of the present invention is to provide a method and an apparatus for viscous processing wherein a processing composition of relatively low viscosity, say from 30 to 50 centipoises at 25 to 55 C., may be used.

A further object is to provide an apparatus for viscous processing wherein the atmosphere in the processing chamber may be accurately controlled so that reproducible results under various conditions of ambient temperature and humidity may be obtained.

According to the present invention, the method for processing an exposed photographic web comprises the steps of applying processing composition in a thin layer to the web, maintaining the web in a processing zone wherein the atmosphere is maintained at a substantially constant wet bulb temperature and removing the processing composition from the web after it has remained a determined time thereon, the relative humidity of said atmosphere being not higher than the relative humidity with which the processing composition applied to the web is in equilibrium. By the term equilibrium used herein is meant that the relative humidity of the atmosphere is such that there is no transfer of water to or from the layer when the layer is in contact with the said at mosphere.

As a consequence of the relative humidity of the atmosphere in the processing zone being equal to or lower than the relative humidity with which the processing composition is in equilibrium, the applied composition does not take up moisture from the surrounding atmosphere and thus does not become diluted. In that way, it may have a viscosity as low as the values mentioned hereinbefore, without the risk of causing undesired effects.

Since conventional photographic processing solutions are in equilibrium with a relative humidity of about 90 percent, the relative humidity of the processing atmosphere is preferably between 70 and percent.

Preferred steps in the method according to the invention are as follows.

A humidifying liquid is heated, the atmosphere in a humidifying zone is humidified by spraying an excess of said heated liquid in said zone so that the atmos here comes substantially into equilibrium with the vapor pressure of the hea ed liquid, the wet bulb temperature of said humidified atmosphere being lower and the relative humidity thereof being higher than the final values thereof in the processing zone, said humidified atmosphere is heated thereafter in a heating zone, and a strong stream of said humidified and heated atmosphere is circulated through the processing zone to maintain the relative humidity therein at a value equal to or lower than that required to maintain the equilibrium. The excess of humidifying liquid in the humidifying zone is collected at the entrance of said zone, and the heating of the humidifying liquid is controlled as a function of the temperature of said collected excess of humidifying liquid.

The heating of the humidified atmosphere in the heating zone is controlled as a function of the dry bulb temperature of the atmosphere measured in the processing zone.

The humidifying liquid is an aqueous solution, the concentration of the dissolved substance(s) of which is lower than the value for which the said solution is in equilibrium with the relative humidity in the processing zone at the required wet bulb temperature.

The humidifying liquid is heated, the atmosphere in a humidifying zone is humidified by spraying an excess of said heated liquid in said zone so that the atmosphere comes substantially into equilibrium with the vapor pressure of the heated liquid, and a strong circulation of said humidified and heated atmosphere is caused through the processing zone, the said liquid being an aqueous solution, and the concentration of the dissolved substance(s) being such that at the temperature the atmosphere is humidified, and which directly determines the wet bulb temperature of said atmosphere in the processing zone, the relative humidity of the atmosphere is lower than the relative humidity with which the processing composition is in equilibrium.

A web-processing apparatus of the type wherein the processing composition is applied in a finite layer onto a continuously advancing web, and wherein said web and said ap plied processing composition remain for a predetermined period in a processing chamber, may comprise the following means for maintaining the atmosphere in said processing chamber at a substantially constant wet bulb temperature: a humidifier for introducing an excess of water in an atmosphere so that the atmosphere comes substantially into equilibrium with the water vapor pressure, first heater means for heating said water which is fed to said humidifier to a temperature so that the wet bulb temperature of the humidified atmosphere is lower than that required in the processing chamber, a sink for collecting the excess of water from the humidifier, and pump means for pumping the water from said sink through said first heater means to said humidifier, second heater means for increasing the temperature of the humidified atmosphere, and blower means for circulating said humidified and heated atmosphere through the processing chamberand than back again to said humidifi Although in the present description the term processing will be mainly used for indicating the step of developing an imagewise exposed photographic film, it is to be understood that said term includes also other steps in the conventional wet treatment of photographic webs, such as the fixing, the bleaching, etc.

The invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic longitudinal view of a processing apparatus,

FIG. 2 is the device for humidifying and heating the atmosphere fed to the developing chamber,

FIG. 3 is the feed circuit of the developer composition,

FIG. 4 is the electric circuit of the heating means controlling the atmosphere fed to the developing chamber,

FIG. 5 is a psychometric chart.

The processing apparatus shown in FIG. 1, comprises a rectangular housing including a feed chamber 11, a viscous developing chamber 12, a fixing chamber 13, a rinsing chamber 14, and a drying chamber 15. Chambers 11 and 12 are accessible through hinged doors fitted at a lateral side of the apparatus. Liquid and electric supply means, as well as the arrangement controlling the atmosphere in the processing chamber are located in a housing (not shown) which is placed next to the housing 10.

The exposed film 17 is supplied to the apparatus from a magazine 18 which is releaseably secured to a support 19. The film is transported from magazine 18 over idler roller 20, around a pivotable mounted end-of-roll detector roller 21, a rubber-covered transport roller 22, and an idler roller 23. A spring-biased and pivoted pressure roller 24 ensures the firm contact of the film with the periphery of transport roller 22. A rectangular shield 25 traps the light which might enter the apparatus through opening 26 when a magazine is being changed, or replaced for attaching a leader belt to the film as will be described later on.

The end-of-roll detector roller 21 is pulled by the film, when tensioned, to a lower position wherein an end-of-roll detector switch (not shown) which controls the motors driving the transport rollers, is closed.

The transport roller 22 is driven by a separate motor, which may rotate at a rigorously constant speed.

Through transversely extending slot 27 the film is passed into the developing chamber 12. In said chamber, the film is led over development backing roller 28, and then passed in a helicoidal loop around free-rotating rollers 29 and 30. Roller 30 is journaled in a bearing 31 which is mounted for vertical displacement, so that the length of the loop formed by rollers 29 and 30 is adjustable to permit the setting of the time for development. The developer composition is applied to the film from an extrusion coating hopper 32. The developer composition is fed to the hopper from a container 70 (FIG. 3) by a metering pump 71. The composition is forced through a heat exchanger 72 which is fed with heated water, the temperature of which is kept thermostatically constant.

Chamber 12 is thermically insulated, and care has been taken to exclude almost any leakage of air, except through entrance opening 27 and outlet opening 37. The air conditioned by the device, shown in FIG. 2, enters in the developing chamber through opening 33 and is carried off through opening 34. Openings 33 and 34 are largely dimensioned so that the velocity of the conditioned air forced through the chamber 12 is in any point almost equal.

When leaving the developing chamber 12, through opening 37 the film describes a loop over rollers 35 and 36 before entering the fixing solution 38. At one side of the loop formed by rollers 35 and 36, a water spray nozzle 40 is provided for the removal of the coating of developer composition from the film surface. The water and the removed developer are collected at the bottom of the small tank 41 and carried off through a conduit, not shown.

The film describes helicoidal loops in the body of fixing solution 38 in chamber 13 around roller sets 42 and 43 which each comprise several free rotating rollers which are spaced axially in side-by-side relationship. A conventional replenishment arrangement is provided (not shown) for replenishing the fixing composition.

Thereupon, the film is passed through the rinsing chamber 14 where it forms in the rinsing bath 44 several loops on roller sets 45 and 46.

Finally, the film passes through the drying chamber 15 where rows of transversely extending blower tubes 47, 48 direct streams of hot air onto the film. The film is gripped between roller pair 49 which is driven by a torque motor, and is led out of the apparatus in the direction of the arrow, whereafter it may be rolled up.

The device for conditioning the air which is fed to the developing chamber is shown in FIG. 2.

It comprises a conditioning chamber 50 in the form of a thermically insulated column, which is provided with an inlet conduit 51 and an outlet conduit 52. This conduit 52 is connected with the inlet opening 33 of chamber 12, whereas the outlet opening 34 of said chamber is connected by a conduit 53, through an air compressor 54, with the inlet conduit 51. The conduit 53 is further provided with a small pipe 65 through which ambient air may be aspirated. In the mentioned way a slight overpressure will be established in the developing chamber 12, since the quantum of air introduced in the chamber 12 is greater than the quantum removed through conduit 53. The overpressure compensates for losses of air through leakages of the circuit, such as the openings 27 and 37, and it prevents the uncontrolled entering of ambient air through air leakages in the circuit.

The bottom of chamber 50 forms a sink 55 for collecting the excess of humidifying liquid. Said liquid is sprayed into the chamber by a humidifier comprising four downwardly directed spray nozzles 56. The water supplied to said nozzles is heated in a first electric heater 57 to which it is fed by a pump 58. The pump is supplied with water from line 59 through which the sink 55 communicates with a constant level tank 60.

The object of the water supply from tank till is to compensate for small losses of moisture in the circuit of the device 50 and the chamber l2, as a consequence of air leakages in said circuit.

The liquid level in tank 60 and consequently also in the sink 55, is determined by an overflow pipe til. A water supply represented by the block 62, which supply may actually be conventional tap water, is provided to deliver through a valve 63 a constant duty of water to the tank 60.

A second electric heater 68 is located in the chamber 50 above the humidifier and increases the temperature of the humidified atmosphere.

The heater 57 is thermostatically controlled (FIG. 4) by a temperature-sensitive switch 67 which is dipped into the liquid collected in the sink 55. The heater 68 is controlled by a temperature-sensitive switch 78 which is located in the developing chamber 12 near the area where the developer composition becomes coated on the film.

The functioning of the device in normal operation will now be described.

In said description, the meaning of the symbols is as follows:

t, temperature at which the water, heated by the first heater 57, is fed to the spray nozzles 56 2,, temperature of the excess of humidifying water, collected in the sink 55,

t= dry bulb temperature of the atmosphere at a given stage,

t wet bulb temperature of the atmosphere at a given stage,

r.h. relative humidity in percent.

As to the temperature t virtually it is the temperature at which the humidifying of the atmosphere has taken place. In case the atmosphere has been saturated with water, said temperature t corresponds substantially with the dry as well as with the wet bulb temperature of the atmosphere. In case the humidifying liquid is an aqueous solution as will be described further in the description, said temperature t corresponds with the dry bulb temperature of he atmosphere.

The psychometric chart shown in HQ. 5, to which will be referred in the description hereinafter and which is drawn for a barometric pressure of 760 mm. Hg, includes relative humidity curves from percent to 100 percent, the moisture content being read on the abscissa in grams of water vapor per kilogram of dry air, the dry and wet bulb temperatures being read on the ordinate in C. Lines (a) point to constant wet bulb temperatures.

The device functioning in normal operation, the amount of air forced by the blower 54 to the chamber 50 and the amount of water sprayed into the chamber, per unit of time, are substantially constant. An excess of water is sprayed into the chamber so that the atmosphere comes into equilibrium with the vapo. pressure of the water.

If, for instance, the temperature at which the atmosphere is moistened by the nozzles 56 is 285 C. and g. of water are taken up by 1 kg. of air, the point A may be marked on the curve 100 percent. The temperature at which the water was fed to the spray nozzles amounted to 30.5" C.

After humidifying, the atmosphere passes through the heating zone where the heater 63 increases the dry bulb temperature of the atmosphere to, for instance, C. Since the moisture content does not change, the point B may be drawn on the chart. it is seen that the relative humidity has dropped to 70 percent. The wet bulb temperature is read in drawing through point B a line, running parallel to lines (a) of constant wet bulb temperature, which intersects the curve 100 percent humidity in point C. The wet bulb temperature corresponding with point C amounts to 30 C. (see also the first two columns of the table hereinafter).

Thus the parameters of the atmosphere which is conducted through pipe 52 to the developing chamber 12 are as follows:

r.h.=70 percent The control of said atmosphere through the thermostatic switches 67 and 73 occurs as follows.

Thermostat 67 measures the temperature of the excess of humidifying liquid collected in the sink 55. As said already hereinbefore, said temperature corresponds within close limits, say within 0. 1 C., with the wet bulb temperature of the atmosphere in the humidiiying zone. When the temperature of the water in the sink 55 lowers, thermostat 67 will control heater $7 to increase the temperature i of the water fed to the spray nozzles, thereby keeping the moisture content of the humidified air constant.

The lowering of temperature t of the water collected in the sink 55 may be due to a decrease in temperature of the water supplied from tank fill, or to a decrease in temperature of the ambient air which through pipe 65 is introduced into the circuit.

Since the amount of water supplied from tank 60 is rather small compared to the amount of water supplied from the sink 55 and, moreover, the temperature of the water from supply 62 remains practically constant within close limits, fluctuations in temperature caused by the water supply 62 are very small.

The temperature of the ambient air which is introduced in the circuit is almost without any importance. This becomes clear when the heat capacity of air is compared with the heat capacity required for evaporating the humidifying liquid, viz 0.24 Kcal. per C. per m. of air, versus 0575 Kcal. per gram of water. The evaporation of the amount of water thus largely determines the temperature of the air. Finally, the amount of air introduced through pipe 65 is only about 1/ th of the amount of air passing through conduit 53.

Since the thermostat 67 is dipped into a body of liquid, its response time is short, so that an accurate control of the temperature of the atmosphere is obtained.

Thermostat 78 measures the dry bulb temperature of the humidified air entering the developing chamber, and controls the heater 68. Normally spoken, the wet bulb temperature should be measured in the developing chamber since said temperature is directly responsible for the cooling of the viscous layer during development as a consequence of evaporation. However, measuring the dry bulb temperature offers several advantages.

The response time of a dry bulb thermometer is faster than that of a wet bulb thermometer.

The controlling of the dry bulb temperature offers in the present case an accuracy of the wet bulb temperature, which is about four times greater. This becomes clear when considering a change of point B on the psychometric chart. If the dry bulb temperature is increased, say by 1 C., the corresponding wet bulb temperature increases by 0.25 C., the moisture content of 25 g. remaining unchanged. It thus the thermostat "78 offers an accuracy ofeg. 0.4 C., changes in the wet bulb temperature of the atmosphere in the developing zone will generally not exceed O.l C. The difference in dry bulb temperature for a given difference in wet bulb temperature increases even when the temperature is increased, since the slope of the curves of relative humidity decreases or higher temperatures.

In keeping the air velocity in the developing chamber relatively high, say greater than 20 m./min., the difference in temperature of the entering and the leaving air is neglectable, say smaller than 0.5 C.

According to a particular measure, developer composition was applied to the film at a temperature which as from 1 C. to several degrees higher than the wet bulb temperature of the processing atmosphere. As a consequence of evaporation, the applied development layer rapidly cools down until it attains the wet bulb temperature in the chamber. Any further evaporation occurs at said temperature. When the situation would be reversed and the temperature of the atmosphere would be higher than that of the coated layer of developer composition, the temperature of the developer composition would slowly increase as a consequence of the poor heat transfer from the atmosphere to the liquid layer.

In the operation of the processing apparatus, after the film is unwound from the core of magazine 18, the film tension is lost causing the spring-biased detector roller 21 to lift. Thereby the end-of-roll switch controlled by the roller 21 is opened so that the electric circuit of the motors driving the transport roller 22 and the pulling rollers 49 are opened, and the film transport is arrested. Further, the metering pump 71 is arrested. The operator removes the magazine, splices the end of a leader belt to the end of the film and starts again the driving of the apparatus. The remaining portion of the film and the leader are transported through the apparatus until the end of the leader releases the roller 21 so that the apparatus is arrested again. The leading end of a new film may now be spliced to the trailing leader portion.

During said different operations, it may be preferred to per form one or more cleaning operations of the apparatus. To this end pressurized water may be fed to spray nozzles (not shown) located in the developing chamber for cleaning the hopper, the rollers, etc. Through a valve (not shown) provided in the conduit between the heat-exchanger 72 and the hopper 32, a supply of cleaning water may be connected to the hopper in order to remove the rest of developer composition from the conduit and to clean the hopper. These and other measures for the treatment of the apparatus in the standby position, during the film changing, etc., are deemed to be known by those skilled in the art. Said measures do not directly relate to the gist of the invention, and are not further discussed hereinmer.

In order to have a more precise insight on the device for controlling the processing atmosphere described hereinbefore, the values of some parameters are given hereinafter.

Volume of developing chamber 12 200 dm.

Volume of chamber 50: 100 dm.

Duty of blower 54: m. /min.

Ratio of the air volume passing through pipe 65 to the air volume passing through conduit 53 l to 100.

Quantum ofwater fed to nozzles 56 l dmP/min.

Power of heater 57 1,000 watt.

Power of heater 68 1,000 watt.

Development time, adjustable (roller 30) between 5 and 15 see.

In the operation of the apparatus, it was noted that under various conditions of the ambient air, the development results were markedly uniform over periods ranging even over a full working day.

It should be remembered that in the mentioned interval of the time, the conditions in the room where the processing apparatus is mounted may change considerably. The apparatus introduces a considerable amount of moisture into the air so that the relative humidity of the ambient air, which was e.g. 50 percent at the start of the processing, increases to 65 percent or more. Moreover, at the moment the apparatus is started, in the morning, the room temperature is relatively low but after a few hours, as a consequence of heat losses of the processing apparatus and of the heat exchangers, and occasionally also of the local room heating, the room temperature may increase considerably. I t

The arrangement of the device for controlling the temperature and humidity of the atmosphere is not limited to the described embodiment.

The operations of humidifying and heating may occur in two separate chambers which are connected with each other through a thermically insulated conduit.

The thermostatic control of the heaters 57 and 68 may occur more accurately in replacing the discontinuously operating control circuit, comprising the thermostatic switches 67 and 78, by a proportionally operating control system.

When the temperature of the water from supply 62 is yet subject to considerable fluctuations causing difficulties in the control of the atmosphere in the device 50, the temperature of said water may be thermostatically controlled.

In order to ensure a good mixing of the water supplied from tank 60 with the water collected in sink 55, a stirrer may be provided in the body of liquid in the sink 55 and the pump 58 may be connected directly to the sink 55 instead of to the conduit 59.

So far, the description related only to the controlling of the processing atmosphere in a closed circuit. It is evident that this is not a condition required per se, and that the apparatus and the method according to the invention may also be used in an open circuit. The control of the atmosphere in an open circuit, however, requires a humidifier 56 and a heater 68 of considerably greater capacity and even then the accuracy of the control will be inferior to that obtained in a closed circuit wherein, especially when heat and air leakages are kept low, after a few minutes uniform working conditions have established.

According to a particular step of the method described hereinbefore, an aqueous solution instead of water is fed to the humidifier for moistening the air.

As known, the boiling point of water, and more generally, of any solvent, is elevated by the addition thereto of a dissolved substance. For instance, an aqueous salt solution containing 4 moles of sodium chloride per litre of water has a boiling point of 104 C. As a consequence of this increase of 4 C. in boiling temperature, an atmosphere which is saturated with said salt solution is in equilibrium with a relative humidity of less than 100 percent.

The mentioned particular step is illustrated hereinafter with an example, which was carried out in such a way that the conditions obtained in the developing chamber 12 were the same as those obtained according to the example described hereinbefore, wherein the humidifying was done by spraying pure water.

The values of the different parameters are given in the third column of the table.

The relative humidity with which the atmosphere saturated with the sodium chloride solution is in equilibrium is determined as follows. The intended moisture content being 25 g./kg., and the air being saturated, the point A may be drawn on the psychometric chart. Since the difference in boiling temperature is 4 C., and the temperature at A is 28.5", the value 28.5+4 determines point D, t=32.5 C., pointing to a relative humidity of percent.

The wet bulb temperature may be obtained in drawing through D a parallel to lines (a), and in reading at the intersection with the curve percent the temperature t'=29.5.

So, in order to obtain the desired wet bulb temperature t= 30 C. and the relative humidity 70 percent, the dry bulb temperature of the humidified atmosphere need only be increased with 35-32.5=2.5 C.

in order to obtain the dry bulb temperature of 32.5 C. of the saturated atmosphere after humidifying, the temperature of the solution fed to the sprayers was: r 345 C.

According to a particular measure, the concentration of the solution fed to the spray nozzles may be chosen in such a way that the saturated atmosphere is directly in equilibrium with the desired relative humidity.

in the case of sodium chloride, the concentration is 6 moles of sodium chloride per litre of water for obtaining a solution which is in equilibrium with about 70 percent relative humidity. it is clear that in using the mentioned solution, the atmosphere must not be heated after it has been humidified since an increase of the temperature would further reduce the relative humidity.

Thus, an aqueous solution containing 6 moles sodium chloride per litre of water is sprayed into the atmosphere at a temperature of about 37 C. (see fourth column of table). The dry bulb temperature of the saturated air is 35, the relative humidity is 70 percent. The humidified atmosphere is passed into the processing chamber without heating, so that the parameters of the atmosphere practically do not change.

In the operation of the apparatus, normally only water vapor leaves the circuit, among others through openings 27 and 37, whereas the salt content remains almost unchanged. it is thus only necessary to control the volume ofwater in the circuit in order to keep the concentration of the aqueous solution constant. The described overflow arrangement provides the mentioned control. It is evident that also other systems may ensure said control and in this respect it may be referred to a float arrangement controlling a valve in the supply of water.

In case a very accurate control of the concentration of the humidifying liquid is required, means may be provided for measuring said concentration and for occasionally controlling the addition to the solution of substances, either in liquid or in solid form, to adjust the boiling point of the liquid.

The application of the invention is not limited to the viscous developing of photographic films but may also be extended to the viscous fixing, bleaching, etc., of photographic film and paper webs.

In the present description, the fixing of the film has been described as occurring in a conventional way because in many important processing installations the recuperation of silver from the used fixing composition is economically interesting.

In smaller installations, more particularly in compact and mobile processing apparatus, however, the fixing and/or other treatments preferably also occur by viscous application.

When thus two or more different viscous treatments have to be performed, these treatments may occur in one chamber wherein different application hoppers and wash'ofi nozzles are provided, or they may be effected in separate chambers and in the latter case the conditioned atmosphere is preferably passed successively through the developing, fixing, bleaching, etc. chambers.

Finally, in connection with viscous processing, reference may be made to the possibility of presoaking the emulsion layer(s) of the film prior to the application of the developer composition. in the mentioned way, the developer penetrates easier through the emulsion layer(s) of the film, and particularly in the case of the multilayer color material, the effective development time of the undermost emulsion layer will equal almost that of the uppermost layer. in the apparatus described, said presoaking may occur for instance during the remaining of the web in the feed chamber ll.

We claim:

1. in a method for processing an exposed photographic web which comprises the steps of applying a processing composition in a thin coating on the web, maintaining the web in a processing zone having an atmosphere maintained at a substantially constant wet bulb temperature, and removing the processing composition from the web after it has remained a predetermined time thereon, the improvement which comprises maintaining the relative humidity of said atmosphere in the processing zone at a value which is not greater than the lid relative humidity at which the processing composition applied to the web is in equilibrium with said atmosphere, wherein said processing zone atmosphere is produced by heating a humidifying liquid, spraying an excess of said heated liquid into the atmosphere of a humidifying zone so that the atmosphere comes substantially into equilibrium with the vapor pressure of the heated liquid, the wet bulb temperature of said humidified atmosphere being lower and the relative humidity thereof being higher than the corresponding values of the atmosphere in the processing zone, heating said humidified atmosphere thereafter in a heating zone, and circulating a strong stream of said humidified and heated atmosphere through the processing zone to maintain the relative humidity therein at a value equal to or lower than that required for maintaining the equilibrium, the excess of humidifying liquid in the humidifying zone being collected at the entrance of said humidifying zone, and the heating of the humidifying liquid being controlled as a function of the temperature of said collected excess of humidifying liquid.

2. Method according to claim 1, wherein the heating of the humidified atmosphere in the heating zone is controlled as a function of the dry bulb temperature of the atmosphere measured in the processing zone.

3. Method according to claim 2, wherein said dry bulb temperature is measured near the point where the processing composition is applied to the web.

4. Method according to claim 1 wherein the humidifying liquid is an aqueous solution containing a dissolved substance at a concentration lower than the value at which the said solution is in equilibrium with the relative humidity in the processing zone at the required wet bulb temperature.

d. Method according to claim l, wherein the circulation of the atmosphere through the humidifying and processing zone occurs in a closed circuit.

6. Method according to claim 5, wherein ambient air is introduced into the closed circuit between the processing zone and the humidifying zone, in order to maintain an overpressure in the circuit.

7. Method according to claim ll, wherein the wet bulb temperature of the atmosphere in the processing zone is about 1 to 5 C. lower than the temperature of the processing composition as it is applied to the web.

8. Web-processing apparatus of the type wherein the processing composition is applied in a thin layer onto a continuously advancing web, and wherein said web and said applied processing composition remain for a predetermined period in a processing chamber, comprising means for maintaining the atmosphere in said processing chamber at a substantially constant wet bulb temperature, comprising: a humidifier for introducing an excess of water in an atmosphere so that the atmosphere comes substantially into equilibrium with the water vapor pressure, first heater means for heating said water which is fed to said humidifier to a temperature so that the wet bulb temperature of the humidified atmosphere is lower than that required in the processing chamber, a sink for collecting the excess of water from the humidifier and pump means for pumping the water from said sink through said first heater means to said humidifier, second heater means for increasing the temperature of the humidified atmosphere, and blower means for circulating said humidified and heated atmosphere through the processing chamber and then back again to said humidifier.

9. An apparatus according to claim 8, wherein water supply and air supply means are provided for compensating losses of humidified atmosphere.

l0. Apparatus according to claim 8, wherein the humiditying and the heating of the atmosphere occur in a chamber separate from the processing chamber.

llll. Apparatus according to claim 8, wherein said blower means circulates the air in a direction opposite to the direction according to which water is sprayed into the air.

l2. Apparatus according to claim 8, wherein said first heater means is thermostatically controlled by sensing means measuring the temperature of the water collected in the sink.

overpressure is maintained in the processing chamber.

16. Apparatus according to claim 8, wherein the thermostatic control of the second heater means is arranged to obtain in the processing chamber a wet bulb temperature which is by 1 to 5 C. lower than the temperature of the developing composition which is applied to the web. 

2. Method according to claim 1, wherein the heating of the humidified atmosphere in the heating zone is controlled as a function of the dry bulb temperature of the atmosphere measured in the processing zone.
 3. Method according to claim 2, wherein said dry bulb temperature is measured near the point where the processing composition is applied to the web.
 4. Method according to claim 1 wherein the humidifying liquid is an aqueous solution containing a dissolved substance at a concentration lower than the value at which the said solution is in equilibrium with the relative humidity in the proCessing zone at the required wet bulb temperature.
 5. Method according to claim 1, wherein the circulation of the atmosphere through the humidifying and processing zone occurs in a closed circuit.
 6. Method according to claim 5, wherein ambient air is introduced into the closed circuit between the processing zone and the humidifying zone, in order to maintain an overpressure in the circuit.
 7. Method according to claim 1, wherein the wet bulb temperature of the atmosphere in the processing zone is about 1 to 5* C. lower than the temperature of the processing composition as it is applied to the web.
 8. Web-processing apparatus of the type wherein the processing composition is applied in a thin layer onto a continuously advancing web, and wherein said web and said applied processing composition remain for a predetermined period in a processing chamber, comprising means for maintaining the atmosphere in said processing chamber at a substantially constant wet bulb temperature, comprising: a humidifier for introducing an excess of water in an atmosphere so that the atmosphere comes substantially into equilibrium with the water vapor pressure, first heater means for heating said water which is fed to said humidifier to a temperature so that the wet bulb temperature of the humidified atmosphere is lower than that required in the processing chamber, a sink for collecting the excess of water from the humidifier and pump means for pumping the water from said sink through said first heater means to said humidifier, second heater means for increasing the temperature of the humidified atmosphere, and blower means for circulating said humidified and heated atmosphere through the processing chamber and then back again to said humidifier.
 9. An apparatus according to claim 8, wherein water supply and air supply means are provided for compensating losses of humidified atmosphere.
 10. Apparatus according to claim 8, wherein the humidifying and the heating of the atmosphere occur in a chamber separate from the processing chamber.
 11. Apparatus according to claim 8, wherein said blower means circulates the air in a direction opposite to the direction according to which water is sprayed into the air.
 12. Apparatus according to claim 8, wherein said first heater means is thermostatically controlled by sensing means measuring the temperature of the water collected in the sink.
 13. Apparatus according to claim 8, wherein said second heater means is controlled by sensing means measuring the dry bulb temperature in the processing chamber.
 14. Apparatus according to statement 13, wherein said sensing means is located near the area where the processing composition is applied to the web.
 15. Apparatus according to claim 8, wherein a continuous overpressure is maintained in the processing chamber.
 16. Apparatus according to claim 8, wherein the thermostatic control of the second heater means is arranged to obtain in the processing chamber a wet bulb temperature which is by 1 to 5* C. lower than the temperature of the developing composition which is applied to the web. 